Internal combustion reciprocating piston engines having corresponding actuator units are known from WO 2011/097298 A1, related to U.S. Pat. No. 8,339,225 and hereby incorporated by reference herein. The actuator unit described therein has actuator pins which are disposed side-by-side and are each slidably supported in a respective housing connected to the actuator unit. The housing is provided at its inner end with conical enlargements which serve to lock the actuator pins in their inner, retracted position and which hold the actuator pins in the spring-loaded position. The guideway between the actuator pins and the housing is cylindrical throughout its entire length to provide efficient and sufficient guidance of the actuator pins within the housing, and thus on the actuator unit.
Due to the cylindrical guideway throughout the length between the housing and the actuator pins, the extension time of the actuator pins is influenced by fluid friction. This influence increases with decreasing temperature. In order to achieve the required extension time at low temperatures, and thus to reach the shift groove at the right time, the force of the springs that extend the actuator pins would have to become disproportionately large. This would also place very high stresses on the locking device.
Increasing the play between the actuator pin and the housing would promote tilting of the actuator pins within the housing, as a result of which an unfavorable line of contact would be formed between the actuator pin and the shift groove or the wall thereof.